The cannon bone is the long bone between the knee or hock and the fetlock, running down the front of the lower leg. It carries weight directly and has little soft-tissue covering, leaving it exposed to splints and knocks. A flat, clean cannon is one of the marks of good lower-leg conformation.
See also: joint just below the cannon, hind-leg joint above the cannon
Further reading: Cannon bone on Wikipedia; disorders of the carpus and metacarpus in the Merck Veterinary Manual.
The poll is the point at the top of a horse head, just behind the ears, where the skull meets the first neck vertebra. It is a sensitive, flexible junction central to how a horse carries its head and yields to the bridle; pressure here from a poorly fitted crownpiece or a harsh hand is a common and often-missed source of resistance.
See also: the forelock that drapes over the poll, paired landmark at the other end of the topline
Further reading: Poll (livestock anatomy) on Wikipedia; physical characteristics of horses from the Merck Veterinary Manual.
The pastern is the sloping region between the fetlock above and the hoof below, made up of the long and short pastern bones. Its angle and length act as a shock absorber: too upright transmits more concussion, too long and sloping strains the tendons. Pastern conformation is a key thing buyers and judges assess.
See also: joint that sits on top of the pastern, trimming affects pastern angle
Further reading: Pastern on Wikipedia; disorders of the fetlock and pastern in the Merck Veterinary Manual.
The frog is the soft, V-shaped, rubbery structure on the underside of a horse hoof, pointing forward from the heels toward the toe. It cushions impact, aids traction, and helps pump blood back up the leg as the hoof flexes under weight. A healthy frog is firm and full; a shrunken or foul-smelling frog often signals thrush.
See also: the structure the frog is part of, trimming and frog health
Further reading: Frog (horse anatomy) on Wikipedia; disorders of the foot in horses in the Merck Veterinary Manual.
The forelock is the lock of mane that falls forward between a horse ears and down the forehead. Anatomically it is the forward continuation of the mane, but it serves the horse by shading the eyes and helping keep flies off the face.
See also: the hair the forelock extends from, the bony point the forelock covers
Further reading: Forelock on Wikipedia; physical characteristics of horses from the Merck Veterinary Manual.
Gastric is an adjective meaning of or relating to the stomach. The term derives from the Greek gaster, meaning stomach. In equine medicine, it appears most commonly in the diagnosis of gastric ulcers , erosions of the stomach lining caused by prolonged exposure to stomach acid , and in the broader category of the broader digestive tract this serves health conditions.
The horse’s stomach is small relative to body size, with a capacity of approximately eight to fifteen liters, designed for continuous small-volume intake rather than large infrequent meals. It is divided into a non-glandular squamous region and a glandular region, each with different mucosal surfaces and acid tolerance. The squamous region, which lacks protective mucus, is the most common site of gastric ulceration in performance horses. Continuous acid secretion, without the buffering effect of constant forage intake, erodes this surface. This is why extended periods without grazing or hay access are a recognized risk factor.
Equine gastric ulcer syndrome is one of the most diagnosed conditions in stabled horses, with studies reporting prevalence of 60 to 90 percent in racehorses and 37 percent in leisure horses. Signs include poor appetite, weight loss, attitude changes, and abdominal pain in the same region symptoms. Diagnosis requires endoscopic examination of the stomach. Treatment with proton pump inhibitors (omeprazole) is well-established; management changes , including increased turnout and continuous forage access , are the primary prevention strategy. Monitoring a horse’s body condition score over time can signal gastric health problems before they become acute.
Further reading: Equine gastric ulcer syndrome on Wikipedia; Gastrointestinal tract at Britannica.
Heme is the iron-containing prosthetic group at the core of hemoglobin, the protein that transports oxygen in red blood cells. Each hemoglobin molecule contains four heme units, and each heme unit holds one iron atom in its center. It is this iron that binds a single molecule of oxygen reversibly , picking it up in the oxygen-rich environment of the lungs and releasing it in the oxygen-poor environment of working muscle tissue.
The iron within heme must be in the ferrous (Fe²⁺) oxidation state to bind oxygen effectively. When iron is oxidized to the ferric (Fe³⁺) state, the resulting compound , methemoglobin , cannot carry oxygen. This oxidative conversion is a toxicological concern in horses exposed to certain plants or drugs that generate oxidative stress; severe methemoglobinemia causes visible cyanosis and exercise intolerance. The color of oxygenated blood (bright red) compared to deoxygenated blood (dark red) reflects the optical properties of heme in its oxygen-bound versus unbound states.
Heme is also the active component of myoglobin, the oxygen-storage protein found in muscle tissue. Horses with a high proportion of oxidative muscle fibers , such as endurance-adapted animals , have denser myoglobin concentrations in their muscles, giving the tissue a deeper red color. Heme degradation products include bilirubin, which is processed by the liver; elevated serum bilirubin in a horse can indicate red blood cell destruction or liver disease that disrupts bilirubin clearance. Assessment of pulse and membrane color as oxygen-saturation proxy and mucous membrane color provides indirect evidence of hemoglobin-oxygen saturation at the clinical level.
The heart is the muscular organ responsible for circulating blood through the body by rhythmic contraction. In the horse, the heart sits within the thoracic cavity, flanked by the lungs, and beats in a regular cycle of contraction (systole) and relaxation (diastole) that drives oxygenated blood to the muscles and returns deoxygenated blood to the lungs via the pulmonary circuit.
A horse’s heart is notably large relative to its body mass , an average adult horse’s heart weighs around 3.5 to 4.5 kilograms (approximately 8 to 10 pounds), compared to 0.3 kilograms in a human. Elite racehorses may carry hearts weighing 5 kilograms or more; the legendary Thoroughbred Secretariat was posthumously found to have a heart estimated at twice normal weight. Heart size is heritable and is one of the factors that distinguishes athletically superior horses at the population level. The left ventricle, which pumps blood to the body at systemic pressure, is particularly developed in fit horses.
Resting beats per minute at rest in a healthy adult horse range from 28 to 44 bpm, lower than the normal human range of 60 to 100 bpm. During intense exercise, a horse’s heart rate can reach 200 to 240 bpm. Deviation from normal resting rate , particularly a rate above 60 bpm at rest , can indicate pain, fever, or cardiovascular compromise; abnormal rhythm detected by a veterinarian via auscultation is one diagnostic indicator for conditions including colic. Heart health is monitored as part of routine veterinary examination throughout the horse’s physical assessment.
In horse anatomy and conformation, an arch is a curved or bowed structure. The term is applied to several distinct anatomical regions, each with its own conformation standards and clinical significance.
The arch of the neck refers to the crest, the dorsal curvature from poll to withers formed by the nuchal ligament and overlying crest muscles. A well-arched neck with a strong, defined crest is considered a mark of quality in many breed standards, particularly in breeds like the American Saddlebred and baroque horses. Excessive cresting (a heavy, pendulous crest that falls to one side) is associated with metabolic conditions including equine metabolic syndrome and pituitary pars intermedia dysfunction (PPID), and should not be confused with ideal conformation.
The arch of the hoof sole describes the concavity of the ground surface of the foot. A properly concave sole (arched away from ground contact) protects the sensitive structures inside the hoof capsule by preventing direct ground pressure on the sole corium. Flat or dropped soles lack this arch and increase sensitivity and bruising risk; a dropped sole in a horse with a history of laminitis indicates chronic structural change from previous rotation. The frog and bars work with the sole arch to absorb and distribute concussion. Farrier evaluation of sole depth and arch is part of routine hoof assessment.
In veterinary and equine surgery, an approach is the defined method by which a surgeon gains access to the target anatomical structure, the sequence of incisions, tissue planes traversed, and structures divided or retracted to expose the operative site. A named approach (lateral approach to the coffin joint, palmar approach to the flexor tendon sheath) specifies not just where to cut but which anatomical landmarks to follow, what to avoid, and how to close.
The choice of approach determines how much visualization the surgeon has, what neurovascular structures are at risk, how much tissue trauma is created, and how the wound will heal. For a given target, such as the hock joint for debridement of an infected joint, multiple approaches may exist with different tradeoffs between exposure and tissue damage. Minimally invasive arthroscopic approaches have replaced open approaches for many joint procedures in horses, reducing recovery time and infection risk compared to open arthrotomy.
The term also appears in a behavioral and training context: the approach phase of training describes the initial step of bringing a horse into proximity with a new stimulus or obstacle, as in trailer loading, where the horse is first rewarded for moving toward the trailer before any other step is asked. In this use, approach is the foundation of approach-retreat desensitization, a systematic method of reducing fear responses. For practical applications see trailer loading problem-solving. Both uses share the core meaning: approach names the way of getting to something, whether a joint or a frightened horse.